Such a sampling device is known, for example, from the journal Jane's NBC Protection Equipment 1992-3, edited by Terry J. Gander, pages 131, 177-179, 181 or from the reprint out of Kampftruppen/Kampfunterstutzungstruppen [Combat Troops/Combat Support Troops], Issue 2/1985, E. S. Mittler & Sohn (publishers), pages 76-79.
An important area of application for the sampling device is the examination of ground contaminated by chemical substances, particularly poisons, warfare agents and the like. For this purpose an analysis unit, for example, a mass spectrometer, is installed in a vehicle encapsulated to the outside. By means of the sampling device chemical substances from outside the vehicle are fed to the analysis unit in such a way that contamination of the inside of the vehicle is impossible. In particular for the chemical sampling of the ground surface over which the vehicle travels, the sampling device can be equipped with one or more sampling wheels which consist essentially of a wheel rim rotating around an axle and a silicone tire fitted onto it. The wheels are attached to a sampling wheel arm, which pivots to bring the wheel into rotatable contact with the ground or places the wheels into various other operational positions, including in front of a sampling head projecting from the vehicle.
In order to carry out continuous measuring of ground samples from a particular stretch that has been covered while the vehicle is in operation, as a rule at least two sampling wheels with sampling wheel arms are employed in tandem operation. In the process one of the sampling wheels rolls over the ground and by means of its silicone tire picks up the substances to be analyzed, while the other sampling wheel is in a raised tracing position in front of the probe head of a sampling probe, which transfers most of the sample substances that have been collected in the silicone tires, to the analysis unit in the interior of the vehicle.
Since in the process of operation the silicone tires of the sampling wheels can in part become considerably contaminated, it is necessary to replace the sampling wheels relatively often. For this purpose as a rule several spare sampling wheels are carried along in the vehicle. These are generally stored in a closed, cylindrical container. Similar storage containers for sampling wheels are also used for long-term storage of sampling wheels outside of the vehicle.
A significant disadvantage of the previously known sampling wheels is found in the fact that until now a synthetic material was always used in the production of the wheel rim. Over a longer period of time, however, the conventional plastic rims in the gastight storage container, generally a 10-pack-can, volatilize monomers and oligomeres of the synthetic materials used for the plastic rims. During what is normally years of storage in the storage container, which typically has a gas volume of about 3-4 liters, the vapors accumulate up to a concentration of approximately 30 ppm.
The silicone tires of the sampling wheels, which must show a high degree of acceptance for chemical substances, in turn take up to a great extent the vapors from the plastic rims so that the sampling wheels are already considerably contaminated before their actual use. These chemical substances released from the plastic rims create an extremely interfering background for the measuring signal. A consequence thereof is a significant decrease to the sensitivity of the analysis unit with regard to the substances to be monitored in the course of operation.
Therefore, the present invention is to introduce a sampling device with a sampling wheel of the kind described above, for which such a contamination of the silicone tire is impossible during the long-term storage in a storage container. At the same time, however, the sampling wheel as a mass product is to be easily and inexpensively produced, and it must stand up to the stresses of operation, i.e., be able to tolerate running speeds of up to 100 km/h.